Serialization: embrace whitespace

[mtias]

Let's try to make the final output (and text view) a bit more readable if we can with line breaks, etc.

[jasmussen]

Just a few linebreaks between blocks would make a world of a difference.

[nylen]

I think we should probably go even further than this and make the parsing + serialization mechanisms remember and preserve the amount of whitespace present in the post content.